Activity of quinupristin-dalfopristin in invasive isolates of Streptococcus pneumoniae from Italy

Dominance of multidrug resistant CC271 clones in macrolide-resistant streptococcus pneumoniae in Arizona

BACKGROUND

Rates of resistance to macrolide antibiotics in Streptococcus pneumoniae are rising around the world due to the spread of mobile genetic elements harboring mef(E) and erm(B) genes and post-vaccine clonal expansion of strains that carry them.

RESULTS

Characterization of 592 clinical isolates collected in Arizona over a 10 year period shows 23.6% are macrolide resistant. The largest portion of the macrolide-resistant population, 52%, is dual mef(E)/erm(B)-positive. All dual-positive isolates are multidrug-resistant clonal lineages of Taiwan19F-14, mostly multilocus sequence type 320, carrying the recently described transposon Tn2010. The remainder of the macrolide resistant S. pneumoniae collection includes 31% mef(E)-positive, and 9% erm(B)-positive strains.

CONCLUSIONS

The dual-positive, multidrug-resistant S. pneumoniae clones have likely expanded by switching to non-vaccine serotypes after the heptavalent pneumococcal conjugate vaccine release, and their success limits therapy options. This upsurge could have a considerable clinical impact in Arizona.

Evolution of erythromycin resistance in Streptococcus pneumoniae in Italy

OBJECTIVES

To evaluate erythromycin resistance in recent invasive isolates of Streptococcus pneumoniae in Italy, to study the phenotypic and genotypic characteristics of the isolates, and to compare data with those obtained in a previous survey.

METHODS

Invasive pneumococcal isolates were obtained from 56 laboratories throughout the country, in 2001-2003. Isolates were serotyped and antimicrobial susceptibilities determined by Sensititre panels and Etest. A new PCR was performed to detect erythromycin resistance genes. Typing methods for selected erythromycin-resistant isolates included PFGE and multilocus sequence typing (MLST).

RESULTS

One hundred and fifty-five isolates out of 444 (34.9%) were resistant to erythromycin: 95 isolates (21.4%) carried erm(B), 56 (12.6%) carried mef(A) and three carried both genes. One isolate, carrying neither erm(B) nor mef(A), showed a point mutation in domain V of the 23S rRNA genes. The mef(A)-positive isolates carried subtype mef(A) (47 isolates), subtype mef(E) (nine isolates), and both subtype mef(E) and erm(B) (three isolates). All subtype mef(A) strains, except two, belonged to serotype 14, appeared to be clonally related by PFGE and related to the England14-9 clone by MLST. The two isolates belonging to other serotypes showed different genetic backgrounds.

CONCLUSIONS

Erythromycin resistance in S. pneumoniae has increased in the last few years in Italy. erm(B) is still the predominant resistance determinant; however, the increase in erythromycin resistance (34.9% versus 28.8% of the previous years) is mainly due to an increase in the proportion of isolates carrying the efflux pump mef(A), whereas the proportion of isolates carrying erm(B) has not changed.

Phenotypic and genotypic characterization of two penicillin-susceptible serotype 6B Streptococcus pneumoniae clones circulating in Italy

Twenty-nine penicillin-susceptible serotype 6B strains isolated from patients with invasive diseases and from healthy carriers were examined by different genotyping methods. Ten groups were identified on the basis of the pulsed-field gel electrophoresis (PFGE) profiles, and two of these contained multiple isolates and were analyzed further. PFGE group 1 comprised 12 isolates, the majority of which had a multiresistant phenotype (resistance to erythromycin, clindamycin, tetracycline, chloramphenicol, and trimethoprim-sulfamethoxazole), corresponding to that of a clone previously described in the Mediterranean area and related to penicillin-resistant clone Spain(6B)-2. The pbp2b, pbp2x, dhf, and pspA genes of the isolates had identical restriction profiles; and the partial sequence of pspA was identical to that of clone Spain(6B)-2. In all isolates the resistance determinants erm(B) and tet(M) were inserted in a Tn1545-like element; 11 isolates carried cat as part of the integrated plasmid pC194. Multilocus sequence typing (MLST) performed with two isolates confirmed that their profiles corresponded to that of the Mediterranean clone. PFGE group 2 comprised nine strains, of which the majority showed no antibiotic resistance. Their pspA profiles were different, and the partial sequences obtained for two representative isolates indicated the presence of PspA proteins of different clades. The MLST profile of one strain was identical to that of a serotype 6B strain from the United Kingdom, while two other isolates were novel one-allele variants. This clone appears to be related (five of seven identical alleles) to two other internationally disseminated clones, Hungary(19A)-6 and Poland(23F)-16, both of which are penicillin resistant. The presence of antibiotic-susceptible isolates of this clone suggests that traits other than antibiotic resistance can make a clone successful.